The Effect of WO₃-Doped Soda Lime Silica SLS Waste Glass to Develop Lead-Free Glass as a Shielding Material against Radiation

Abstract

The current study aims to enhance the efficiency of lead-free glass as a shielding material against radiation, solve the problem of the dark brown of bismuth glass, and reduce the accumulation of waste glass disposed in landfills by using soda-lime-silica SLS glass waste. The melt-quenching method was utilized to fabricate (WO${}_3{)}_x$ [(Bi${}_2$O${}_3$)${}_{0.2}$ (ZnO)${}_{0.3}$ (B${}_2$O${}_3$)${}_{0.2}$ (SLS)${}_{0.3}$]${}_{1-x}$ at 1200 °C, where x = (0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol). Soda lime silica SLS glass waste, which is mostly composed of 74.1 % SiO${}_2$, was used to obtain SiO${}_2$. Radiation Attenuation parameters were investigated using narrow-beam geometry and X-ray fluorescence (XRF). Furthermore, the parameters related to radiation shielding were calculated. The results showed that when WO${}_3$ concentration was increased, the half-value layer was reduced, whereas the $\mu$ increased. It could be concluded that WBiBZn-SLS glass is a good shielding material against radiation, nontoxic, and transparent to visible light.

1. Introduction

Radiation is defined as the energy that is emitted from a source and passes through space penetrating a variety of materials. It may also be utilized in a variety of applications, such as radiation therapy, agriculture, industry, radioisotope projects, and particle accelerators. However, the several advantages of radiation may be quite hazardous when exposed to large doses that are above the safe limits. To manage the radiation dose at a safe level, researchers are focused on radiation shielding materials [1,2,3]. Radiation shielding depends on the attenuation principle, which is the ability to absorb or attenuate radiation. Radiation shielding materials can be defined as protective materials to reduce exposure to radiation by placing material between the radiation source and a person. Concrete is considered to be a conventional and economical technique used for shielding purposes. Concrete is efficient and cheap, and can be easily shaped into any desired design [4]. However, there are some limitations related to concrete, such as its opacity, preventing visible light from passing through, and its mechanical strength being reduced when exposed to radiation for a longer period of time [5,6,7,8]. Glass is a type of radiation shielding material that can be an alternative to concrete for protection from radiation risks due to its remarkable chemical and physical properties, such as excellent optical transparency to visible light, simplicity of manufacturing, nontoxicity, low cost, and its physical characteristics, such as density and effective atomic number, can be changed by inserting heavy metal oxides into the glass network for use as radiation shielding material [9,10,11].

Recently, researchers have focused on the preparation of heavy metal oxide glass such as PbO, BaO, and Bi${}_2$O${}_3$ for use as radiation shielding material because they possess desirable features such as high density, strong nonlinear optical susceptibility, and excellent $\gamma$-ray shielding [12,13,14,15]. PbO-based glasses have high density and are favorable in many applications [16,17]. However, PbO glass is limited due to its toxicity to human health and the environment. Consequently, researchers have focused ecofriendly alternatives such as Bi${}_2$O${}_3$ instead of lead’s environmental toxicity [18,19,20]. Bi${}_2$O${}_3$ glass is considered to be a suitable alternative to PbO glasses to use in radiation shielding implementations due to its unique characteristics such as high radiation protection, high density, high refractive index, and nontoxicity [21]. Glass containing Bi${}_2$O${}_3$ is a good option for radiation protection. This result is consistent with a number of studies [21,22,23,24]. High concentrations of Bi${}_2$O${}_3$ in glass modify the colour of the glass, turning it dark brown or black, and raise the melting temperature [25]. Material scientists and glass developers are facing technical challenges in developing high-transmission Bi${}_2$O${}_3$ glass.

Manufacturing industries play a significant role in economic growth. This industrialization produces an enormous amount of solid waste that causes environmental problems due to the accumulation of waste and limited landfill sites. To solve these problems, researchers are focused on treating and converting solid waste into more valuable and environmentally friendly materials [26,27,28]. Glass is an example of solid waste that needs long periods of time to decompose. For this reason, there is much interest in using glass as an alternative source of SiO${}_2$, and in reusing silica-rich waste such as clamshells, eggshells, fly ash, and soda–lime–silica (SLS) to reduce high-cost chemical materials and dispose of waste [28,29,30]. SLS glass is widely used as windowpanes glass containers and flat glass or container wares. SLS glass is preferred when compared to conventional glass because it has a good glass-forming nature and is composed of SiO${}_2$, Na${}_2$O, CaO, MgO, and Al${}_2$O${}_3$; so, much research uses SLS as an alternative source of silicon [31,32,33,34,35].

The current work aims to use soda–lime–silica waste glass SLS in order to prepare a lead-free glass radiation shield, it is necessary to decrease the buildup of SLS glass waste and manufacturing expenses, and improve its efficiency to attenuate photon intensity, which can be used as radiation protection in addition to increasing the optical characteristics of glass samples by decreasing their dark brown or black color. The linear, mass attenuation coefficients, and other parameters related to attenuation studies were investigated.

2. Materials and Methods

2.1. Glass Preparation

In this work, SLS glass waste was used as an alternative source of silicon SiO${}_2$ by crushing it into powder using a mortar and pestle. Chemical powders such as Bi${}_2$O${}_3$, ZnO, B${}_2$O${}_3$, and WO${}_3$ were used to prepare glass samples with composition (WO${}_3$)${}_x$[(Bi${}_2$O${}_3$)${}_{0.2}$ (ZnO)${}_{0.3}$ (B${}_2$O${}_3$)${}_{0.2}$ (SLS)${}_{0.3}$]${}_{1-x}$, where x = (0, 0.01, 0.02, 0.03, 0.04 and 0.05 mol). The melt-quenching method was utilized to fabricate the glass samples. The chemical powders were blended, thoroughly crushed for 10 min in a mortar and pestle, and transported to an alumina crucible. After that, the crucible was placed in the electric furnace where the temperature of the furnace progressively rose to 1200 °C at a rate of 10 °C/min and was held for 1.5 h for melting. After that, the molten mixture was poured into a preheated cylinder brass plate and annealed for about 1 hour at approximately 350 °C in order to avoid strains and internal mechanical stress. Lastly, samples were polished to evaluate the characteristics of the glass after cooling to room temperature. These glass types have a thickness of 6 mm, and were labeled CS, W1, W2, W3, W4, and W5, which correspond to doping levels of 0, 0.01, 0.02, 0.03, 0.04 and 0.05 mol WO${}_3$, respectively (as shown in Figure 1).

2.2. Physical Properties

Density is one of the physical characteristics that may be used to investigate changes in glass structure. It is influenced by structural rigidity and variations in geometric configuration. Density was measured according to the Archimedes principle using the following formula [36]:

$$\rho =\frac{a}{a-b}{\rho }_{distilledwater}$$

(1)

where ${\rho }_{\left(distilledwater\right)}$ is distilled water density, a is the weight of the glass sample in air, and b is the weight of the glass sample in distilled water. The molar volume is $V_m$ and oxygen packing density is OPD. $V_m$ was calculated using the following equation [37].

$$V_m=\frac{M_{wt}}{\rho }$$

(2)

Oxygen packing density OPD provides information about the glass network’s tightness. The OPD is measured utilizing the following equation:

$$OPD=1000\times \frac{c}{V_m}$$

(3)

where c is the total number of oxygen atoms. Additional physical characteristics, including the ion concentration (N), polaron radius ($r_p$), internuclear separation ($r_i$), and field strength (F) were measured for all the fabricated glass samples using the following formulas [38].

$$N=(mole\%)\frac{N_A\rho }{M_{wt}}$$

(4)

$$r_p=\frac{1}{2}{\left(\frac{\pi }{6N}\right)}^{\frac{1}{3}}$$

(5)

$$r_i={\left(\frac{1}{N}\right)}^{\frac{1}{3}}$$

(6)

$$F=\frac{Z}{r_p^2}$$

(7)

2.3. Radiation Attenuation

The radiation parameters were calculated theoretically depending on the formulas explained in previous literature [18,39].

The experimental linear attenuation coefficient $\mu$, mass attenuation coefficient ${\mu }_m$ values of the prepared glass were measured using (XRF) and narrow-beam gamma-ray transmission geometry.

Figure 2 illustrates the experimental setup of prepared glass attenuation using narrow-beam gamma-ray transmission geometry [39].

The source activity of Am-241 was 45 $\mu$ Ci, while the Cs-137 and Co-60 source activities were 5 $\mu$ Ci. Gamma rays from Am-241, Cs-137, and Co-60 of were used as point sources to emit photons with different energies.

The $\mu$ of glass samples was determined employing X-ray fluorescent equipment (XRF). The high-purity metal plates were composed of the following elements: Nb, Mo, Sn and Pd (see Figure 3). The metal plates are detailed in

Table 1. The plates used in X-ray fluorescence (XRF) experiment.

Plate	Atomic Number (Z)	Thickness (mm)	Purity (%)	$\mathit{K}\mathit{\alpha }1$ Energy (keV)
Niobium (Nb)	41	0.14	99.8	16.61
Molybdenum (Mo)	42	0.11	99.9	17.74
Palladium (Pd)	46	0.1	99.9	21.17
Tin (Sn)	50	0.28	99.999	25.27

.

3. Result and Discussion

3.1. Structural Properties

X-ray fluorescence (XRF) is an effective analytical method for characterizing SLS glass. The chemical compositions of SLS glass samples were determined through XRF analysis and are summarized in

Table 2. Elements included in soda–lime–silica (SLS).

Element	Percentage (%)
SiO${}_2$	74.1
Na${}_2$O	12.91
CaO	9.69
Al${}_2$O${}_3$	1.54
K${}_2$O	0.59
MgO	0.4
P${}_2$O${}_5$	0.02
Fe${}_2$O${}_3$	0.11
TiO${}_2$	0.04
MnO	0.01

. Elements such as SiO${}_2$, Na${}_2$O, CaO, and other minor elements were discovered in the sample. The nature of the WBiZnB-SLS glass samples was determined using their XRD spectra, as seen in Figure 4. All samples had an obvious wide hump and lacked distinct peaks. This demonstrated that all samples were amorphous in nature [40]. EDX analysis results of the WBiZnB-SLS glass samples indicated the existence of tungsten, bismuth, oxygen, zinc, silicon, and boron components, which are shown in Figure 5.

3.2. Physical Properties

The influence of WO${}_3$ on the physical features was evaluated in the present study.

Table 3. Physical properties of WBiZnB-SLS glass.

Measurement	CS	W1	W2	W3	W4	W5
Molecular weight (g)	149.55	150.38	151.20	152.02	152.85	153.67
Density (g/cm${}^3$)	5.16 ± 0.005	5.23 ± 0.004	5.24 ± 0.005	5.28 ± 0.005	5.31 ± 0.006	5.31 ± 0.004
Molar volume (cm${}^3$/mole)	28.96	28.76	28.85	28.78	28.81	28.94
Oxygen Packing Density (g-atom/mole)	72.53	73.33	73.42	73.89	74.14	74.13
W-ion concentration (${10}^{20}$ ion cm${}^{-3}$)	0	2.09	4.18	6.28	8.36	10.41
Internuclear distance(Å)	0	16.84	13.38	11.68	10.61	9.87
Polaron radius(Å)	0	6.79	5.39	4.71	4.28	3.98
Field strength (${10}^{16}$ cm${}^2$)	0	1.61	2.55	3.34	4.05	4.68

shows the various physical parameters of the glass samples. Differences in $\rho$ and $V_m$ with WO${}_3$ concentration are illustrated in Figure 6, which shows that the $\rho$ of the glass samples rose gradually from 5.16 to 5.31 g/cm${}^3$ with the increase in WO${}_3$ content in the glass network. The molar volume also clearly remained approximately constant with increasing WO${}_3$ content. These results can be explained by the dopant of WO${}_3$ (with a molecular weight of 231.84 gmol${}^{-1}$) in Bi${}_2$O${}_3$-ZnO-B${}_2$O${}_3$-SlS glass (with a molecular weight of 149.66 gmol${}^{-1}$). The molar volume was nearly constant. This can be explained by the atomic radius of the W ion (139 pm), which is lower than that of Bi ion (156 pm). WO${}_3$ creates a glass structure that is more compact [41,42,43].

The OPD of the glass samples was determined using Equation (3). According to Table 3, OPD results increased from 72.53 to 74.13 g-atom/mole. This phenomenon could be explained by increasing the amount of nonbridging oxygen in the glass network, leading to an increase in oxygen atoms per unit composition in the glass network. Due to the conversion of [BO${}_3$] structural units into [BO${}_4$] structural units, this resulted in a more compact glass structure, and consequently an increase in glass density [44].

Table 3 display that, when the concentration of W ions in the glass structure increased, the Polaron radius ($r_p$) and internuclear distance ($r_i$) decreased, indicating that the glass network became more compact or stiff owing to the increasing field strength (F) between W ions.

3.3. Attenuation of Gamma Rays

The experimental linear attenuation coefficients for WBiZnB-SLS samples were measured via X-ray fluorescence equipment XRF at photon energies ranging from 16.61 to 25.27 keV, as well as narrow-beam geometry at photon energies ranging from 59.54, 662, and 1333 keV. The $\mu$ and ${\mu }_m$ values are summarized in

Table 4. Linear and mass attenuation coefficients of the current SLS glass system.

	59.54 keV		662 keV		1333 keV
Sample	Linear Attenuation Coefficient $\mathit{\mu }$	Mass Attenuation Coefficient ${\mathit{\mu }}_{\mathit{m}}$	Linear Attenuation Coefficient $\mathit{\mu }$	Mass Attenuation Coefficient ${\mathit{\mu }}_{\mathit{m}}$	Linear Attenuation Coefficient $\mathit{\mu }$	Mass Attenuation Coefficient ${\mathit{\mu }}_{\mathit{m}}$
Cs	14.083	2.727	0.325	0.0630	0.2349	0.0455
W1	14.170	2.710	0.329	0.0628	0.2356	0.0451
W2	14.193	2.708	0.330	0.0629	0.2371	0.0452
W3	14.209	2.690	0.330	0.0625	0.2399	0.0454
W4	14.256	2.687	0.334	0.0630	0.2356	0.0444
W5	14.281	2.689	0.336	0.0632	0.2408	0.0453

. XRF results indicate that the prepared glass samples prevented all photons from reaching the detector. In other words, the glass samples absorbed all photons when the photon energy was less than 25.27 keV.

Table 4 and Figure 7 and Figure 8 show that $\mu$ and ${\mu }_m$ values were reduced as gamma-ray energy increased. $\mu$ and ${\mu }_m$ sharply decreased as gamma-ray energy increased in the low energy range, as the photoelectric effect was responsible for the prominent response between the tested glass samples and gamma rays. The linear and mass attenuation coefficients decreased slightly with increasing gamma-ray energy. This phenomenon can be attributed to the Compton scattering effect. Furthermore, linear values increased with increasing WO${}_3$ content in the glass network. This was due to the increasing glass sample density from 5.16 to 5.31 g/cm${}^3$, and $\mu$ was proportional to the medium density [45,46]. ${\mu }_m$ values declined as the WO${}_3$ content increased, which might be related to the weight fraction of the higher atomic number component (Bi${}_2$O${}_3$) being reduced at the expense of WO${}_3$ [16].

The authors selected various compositions of glass containing heavy metals from previous work, such as 20 Bi${}_2$O${}_3$-20 Na${}_2$O-60 B${}_2$O${}_3$ [47], 30 PbO-10 WO${}_3$-10 Na${}_2$O-10 MgO-40 B${}_2$O${}_3$, [48], 30 BaO-10 Li${}_2\mathrm{O}$-60 B${}_2$O${}_3$ [49], and 20 Bi${}_2$O${}_3$-2 WO${}_3$-20 N$a_2$O${}_2$-58 B${}_2$O${}_3$ glass [50]. The $\mu$ at 59.54 keV was estimated using the Phy-X/PSD software in order to compare the $\mu$ of the present glass to that of other glass samples, as seen in Figure 9. The results indicated that the $\mu$ values in the current work were higher than the $\mu$ values in the previously mentioned studies at an energy of 59.54 keV, and the $\mu$ value of the first glass sample that did not contain WO${}_3$ was less than that of the 20 Bi${}_2$O${}_3$-2 WO${}_3$-20 N$a_2$O${}_2$-58 B${}_2$O${}_3$ glass.

The HVL, MFP, and TVL parameters were considered to be significant in terms of thickness to describe the effectiveness of glass shielding. Figure 10, Figure 11 and Figure 12 illustrate the HVL, TVL, and MFP parameters as a function of WO${}_3$ mole fraction. HVL, TVL, and MFP were reduced when the concentration of WO${}_3$ was raised. This is related to the addition of WO${}_3$ creating a glass structure that was more compact, and increases in both density and $\mu$ values. Despite that, HVL, TVL, and MFP increased as incident photon energy increased. This indicates that the WBiZnB-SLS glass samples were more successful in attenuating gamma radiation at lower energy levels than they were at higher energies. Figure 13 indicates that the relationship between $\mu$ and HVL is inverse, where $\mu$ values decreased as photon energy increased, while HVL values increased.

Moreover, HVL values in the present study were compared with HVL of barite concrete and other glass types at 662 keV. Results indicate that HVL values were smaller than the HVL of barite concrete and other glass types. The HVL values for radiation shielding concrete and glass were previously published [49,51,52,53]. The lower the HVL, TVL, and MFP values of the material were, the more effective the shielding characteristics. This indicates that WBiZnB-SLS glass has better shielding properties and can be used as radiation shielding (see Figure 14).

Gamma radiation interactions, such as scattering and absorption, are related to the materials’ effective atomic number. As shown in

Table 5. HVL (cm), MFP (cm), $Z_{eff}$, and $N_{eff}$(${10}^{23}$) (electrons/g) of glass samples.

	59.54 (keV)				662 (keV)				1333 (keV)
Sample	HVL	MFP	Zeff	Neff	HVL	MFP	Zeff	Neff	HVL	MFP	Zeff	Neff
CS	0.0492	0.0710	63.91	9.007	2.1293	3.0726	24.25	3.406	2.9499	4.2568	20.76	2.9020
W1	0.0489	0.0706	63.95	8.986	2.1087	3.0429	24.32	3.404	2.9410	4.2439	20.83	2.9015
W2	0.0488	0.0705	63.98	8.966	2.1024	3.0337	24.40	3.403	2.9233	4.2183	20.90	2.9010
W3	0.0488	0.0704	64.02	8.946	2.0982	3.0278	24.47	3.401	2.8884	4.1680	20.98	2.9005
W4	0.0486	0.0701	64.06	8.925	2.0741	2.9930	24.55	3.399	2.9410	4.2439	21.05	2.9000
W5	0.0485	0.0700	64.10	8.905	2.0633	2.9774	24.63	3.398	2.8781	4.1531	21.12	2.8995

and Figure 15, the $Z_{eff}$ concentration increased as the WO${}_3$ content increased for all the samples. The atomic number dependency reveals that materials with a high $Z_{eff}$ value attenuate strongly with incoming photons. Moreover, the result indicated a reduction in $Z_{eff}$ as the photon energy increased. At low energies, photoelectric absorption dominated, resulting in a large $Z_{eff}$ value. The $Z_{eff}$ values in the current study were compared to other glass samples at 1333 keV that had been published, as seen in Figure 16 [47,48,50,54]. Research results showed the larger value of $Z_{eff}$ to be more efficient and useful in shielding radiation, as the probability of photon interaction increases with increasing $\mathrm{W}{\mathrm{O}}_3$ concentration, contributing to decreased radiation transmission. Lastly, the effective electron number $N_{eff}$ of the glass samples was calculated and is given in Table 5 at 59.54, 662, and 1333 keV. $N_{eff}$ was nearly constant within the range of 2.89–9.07 ${10}^{23}$ electrons/g and reduced as photon energy increased [55].

4. Conclusions

Glass systems (WO${}_3$)${}_x$[(Bi${}_2$O${}_3$)${}_{0.2}$ (ZnO)${}_{0.3}$ (B${}_2$O${}_3$)${}_{0.2}$ (SLS)${}_{0.3}$]${}_{1-x}$, where x = (0, 0.01, 0.02, 0.03, 0.04 and 0.05 mol), were prepared in order to attenuate gamma radiation intensity. As a result of the XRF analysis, the SLS glass waste contains 74.1 % SiO${}_2$. The amorphous nature of the WBiZnB-SLS glass samples was verified by the XRD data. The results show that when the concentration of WO${}_3$ in the glass increased, glass density increased and both HVL and MFP reduced. Moreover, As gamma-ray energy increased, the ${\mu }_m$, Z${}_{eff}$ and N${}_{eff}$ values decreased. On the other hand, WBiZnB-SLS glass could absorb gamma rays within lower than 25.27 keV. According to current results, WBiZnB-SLS glass is effective at attenuating gamma radiation intensity within the specified energy range and may be used to develop transparent radiation shielding glass.